NMR (Nuclear Magnetic Resonance) spectroscopy is one of the principal techniques used to obtain physical, chemical, electronic and structural information about a molecule. By studying the peaks of nuclear magnetic resonance spectra, skilled chemists are able to determine the structure of many compounds. For example, proton, carbon, nitrogen, and phosphorous NMR spectroscopy are widely used in studies of protein structures. NMR can be a very selective technique, distinguishing among many atoms within a molecule or collection of molecules of the same type but which differ only in terms of their local chemical environment. The most commonly recognized use of NMR is in magnetic resonance imaging for medical diagnosis.
Generally, NMR systems comprise a probe and a console. The NMR probe generally has a NMR probe sensor and NMR probe electronics. The sensor is generally a solenoid or Helmholtz coil. The NMR probe electronics are generally different components for tuning the sensor, including adjustable capacitors, and inductors. The NMR console is generally a computer and radio frequency system capable of producing and detecting a current induced in the NMR probe, specifically the NMR probe sensor. Software on the NMR console constructs a graph of the chemical spectrum.
NMR sensors known in the art include solenoid, Helmholtz, and toroid coils. For example, FIG. 5a shows a solenoid coil 40 useful for recording NMR spectra. A general practice is to place a sample 42 in a sample container 44 at the center of a solenoid coil 40. Sample interrogation produces chemical information about the sample as shown in the NMR spectrum 46 depicted in FIG. 5b. Unfortunately, the NMR spectrum 46 shown in FIG. 5b does not provide information about the location of the sample in the solenoid coil 40. For example, if the sample container 44 is moved towards a winding of the solenoid coil 40 as shown in FIG. 6a, the NMR sensor will produce the NMR spectrum 48 shown in FIG. 6b, which is identical to the NMR spectrum shown in FIG. 5b. Therefore, there is a need for an NMR sensor capable of providing information about the location of the sample in the coil.
Toroid cavity detector (TCD) systems have introduced a radial dimension to NMR sensors, allowing for one-dimensional NMR imaging. For example, U.S. Pat. No. 5,574,370, issued Nov. 12, 1996 to Woelk et al., herein fully incorporated by reference, discloses a toroid cavity detector (TCD) system for determining the spectral properties and distance from a fixed axis for a sample using NMR. The sensor is a toroid cavity with a central conductor oriented along the main axis of the toroid cavity and parallel to a static uniform magnetic field, B0. An RF signal is inputted to the central conductor to produce a magnetic field B1 perpendicular to the central axis of the toroid and whose field strength varies as the inverse of the radial position from the axis of the central conductor within the toroid cavity. The sample is subjected to the respective magnetic fields and the response measured is used by the NMR console to construct an NMR image of the sample adjacent to the central conductor.
The NMR imaging abilities offered by TCD sensors offer numerous advantages. For example, in order to perform imaging with current NMR sensors, external magnet field coils are required to produce magnetic field gradients in the external magnetic field, to cause encoding of the NMR signal, in order to affect images. These expensive gradient coils are not needed to record RFI images with TCDs because the TCD provides a magnetic field gradient itself. In the case of TCDs the gradient is in the RF magnetic field B1 instead of the static magnetic field B0. A gradient in one field or the other is required to affect imaging. With the B1 gradient inherent in a TCD, it is much cheaper to use a TCD for imaging. Unfortunately, a substantial investment is required to replace current NMR sensors with TCDs. Current NMR sensors utilize a coil such as a solenoid or Helmholtz coil, having a relatively large inductance. As a TCD design does not use a coil, but a central conductor having a low inductance, a coil must be added to increase inductance or the NMR sensor tuning circuit needs to be redesigned to account for the lower inductance.
In most cases it is not feasible to increase the inductance of an NMR sensor by adding a coil to the NMR probe. NMR probes are designed to be placed in a compact chamber, where a current in a superconductor solenoid, cooled to extremely low temperatures, produces a strong magnetic field. These probes are designed for maximum efficiency and do not offer room for an additional coil. Furthermore, researchers may be unwilling or unable to retrofit their NMR probes each time they wish to perform NMR imaging.
Furthermore, current NMR sensors provide the desired inductance in a tuned resonant circuit. If a lesser inductance is utilized, the NMR sensor will resonate at a higher than desirable frequency. If the coil resonates at higher frequencies, the higher frequencies may not be suitable for NMR excitation and detection under conditions of the applied static magnetic field, B0. Even if the sample actually receives the higher frequencies, the sample may not adequately respond to the higher frequencies. Furthermore, the high frequencies may interact with the NMR sensor as well as other adjacent systems causing incorrect readings and possibly damage. Therefore, there exists a need for a drop-in-replacement to existing NMR sensors economically enhancing them for NMR imaging.
Current NMR systems utilize thermocouples as an additional component in the NMR probe to indirectly measure the temperature of a sample. This often posses a problem since the NMR probe is confined to a small area. Furthermore, since the sample is often heated or cooled by a focused air stream, the temperature of the thermocouple may be not be indicative of the true temperature of the sample. Therefore, there exists a need for a more direct real time temperature determination of a sample, without requiring additional components.
Therefore, it is an object of one embodiment of the present invention to provide an NMR sensor design that is a drop-in-replacement inductor for existing NMR probes. It is a further object of one embodiment of the present invention for a drop-in-replacement inductor capable of being used for NMR imaging. It is a further object of one embodiment of the present invention to provide a single sensor capable of producing two orthogonal electro-magnetic fields in the same space. Even still, it is an object of one embodiment of the present invention for in situ, accurate temperature measurement of a sample.